Compressed asbestos fiber sheets have been used as gasket material for many years in a variety of industries. Compressed asbestos sheets are prepared by mixing asbestos fibers with a rubber binder to form a dough mixture and pressing the dough mixture under pressure into a uniform product. Typically the sheet is formed on a rubber sheeter or two roll calender, which has one large heated roll and one smaller unheated or cooled roll. The dough mixture is built up on the heated roll while pressing against the cold roll. Laminating occurs as the roll revolves and while the sheet vulcanizes.
Health concerns relating to asbestos have made it desirable to switch to other materials for compressed gasket sheets.
U.S. Pat. No. 4,508,777 to Yamamoto et al discloses a compressed non-asbestos sheet with a high fiber content containing two types of fibers selected from the group consisting of inorganic fibers, other than asbestos or organic fibers.
U.S. Pat. No. 4,859,526 to Potepan et al discloses a high temperature compressed gasket sheet formed from carbon fibers having a carbon content above 90% and, optionally, organic fibers.
A compressed non-asbestos sheet that includes novaloid and aramid fibers, particularly Kynol and Kevlar fibers has not been previously known. U.S. Pat. No. 4,271,228 to Foster et al discloses that novaloid fibers and Kevlar fibers can be used in a fibrous sheet (col. 3, lines 19-48) generally known as a "beater sheet". U.S. Pat. No. 4,851,279 to Das et al mentions that Kynol fibers have been used in gaskets (col. 2, line 24).
Because of the variety of service applications and operating conditions requiring gasketing, there is a need for a compressed non-asbestos sheet that is versatile and can withstand a wide range of fluids at varying temperatures and pressures. In particular, there is a need for a compressed non-asbestos sheet that can withstand demanding operating conditions such as high temperatures and exposure to steam or severe chemicals. Further, there is a need for a compressed non-asbestos sheet that has excellent sealability, flexibility and cutting characteristics.